Cysteine proteinases, which play a role in tissue invasion of host defenses, are a key virulence factor of Entamoeba histolytica. They have shown that purified proteinase of E. histolytica degrade components of the extracllular matrix and cleave IgG, IgA, the C3 and C5 components of complement, and the anaphylatoxin, C3a and C5a. To further understanding of the role of this important virulence factor in invasion, they will use E. dispar and L6, proteinase-deficient Entamoeba as models. E. dispar is morphologically identical and genetically closely related to E. histolytica but releases less cysteine proteinase activity and cannot invade tissue. L6 is an E. histolytica mutant that is defective in phagocytosis and cysteine proteinase activity. They will use this system to test the hypothesis that E. histolytica differs from non-invasive E. dispar or L6 in the quantity, sorting and/or release of cysteine proteinase.